1. Field of the Invention
The present invention relates to a structure of a raw substrate used for manufacturing insulating substrates of a line-type heater used as a heating source or the like in a toner fixing portion of a copying machine or an electrophotographic printer.
2. Description of the Prior Art
Generally, such a line-type heater is well known conventionally, and it is configured such that, for example, as disclosed in JP-A-7-147180, a heating resistance film is formed on the surface of an insulating substrate of ceramic material which is configured, in the form of a long strip so as to extend in a line in the longitudinal direction of the insulating substrate to generate heat from all over its length when a current is supplied to the heating resistance film from the opposite sides thereof.
Conventionally, in manufacturing the line-type heater, such a method has been adopted which comprises the steps of preparing a raw substrate of ceramic material constituted by a plurality of sheets of long strip-like insulating substrates which are put side by side and integrated with each other, forming heating resistance films on places of the surface of the raw substrate correspondingly to the respective insulating substrates, and breaking (dividing) this raw substrate into individual insulating substrate.
When the raw substrate is broken into individual insulating substrates, such a method is adopted which comprises the step of forming a large number of depressed portions (recess portions) of desired depth by radiation of a laser beam in the surface of the raw substrate correspondingly to boundary lines between the individual insulating substrates before or after formation of the heating resistance film so that the depressed portions are arranged in lines at fixed pitch intervals along the boundary lines. Thus, the lines in which the large number of depressed portions are provided are used as scribe lines for breaking the raw substrate into the individual insulating substrates.
However, since the strength of each insulating substrate broken out from the raw substrate in such a manner is uniform at every place all over the length of the insulating substrate, it cannot be expected to generate a crack in the insulating substrate when the temperature of the heating resistance film formed in this insulating substrate becomes an abnormally high value. Therefore, there is a fear that a more abnormally high temperature is brought about.
Therefore, conventionally, at least one small-diameter through hole is formed in a portion on the longitudinal way of the insulating substrate, so that the insulating substrate can crack in the portion of the through hole in case of abnormal temperature to thereby prevent the temperature from increasing more.
In the case where configuration is made such that at least one small-diameter through hole is formed in a portion on the longitudinal way of an insulating substrate, the insulating substrate can crack in the portion of the through hole at the time of abnormal temperature. However the strength of the insulating substrate is reduced extremely in the portion provided with the through hole because the insulating substrate is shaped into a long strip. Accordingly, there has been a problem that the respective insulating substrates are often snapped in their through hole portions when the raw substrate is broken (divided) into individual insulating substrate, or when the respective insulating substrates broken out from the raw substrate are handled ordinarily, for example, carried, attached and so on.
It is an object of the present invention to provide a structure of a raw substrate used for manufacturing line-type heaters which are easy to crack only at abnormally high temperature while keeping usually their strength.
Namely, it is a first technical object of the present invention to provide a structure of a raw substrate by which insulating substrates for use in line-type heaters can be manufactured in such a mode that the insulating substrates are not snapped easily when they are broken out from the raw substrate and when the individual insulating substrates are handled, for example, carried, attached and so on, but any one of the insulating substrate can crack surely only when the temperature of a heating resistance film formed thereon reaches an abnormally high value.
In order to achieve the foregoing technical problems,
a first aspect of the raw substrate is a raw substrate for use for manufacturing insulating substrates in a line-type heater, which comprises a large number of depressed portions formed by radiation of a laser beam in a surface of said raw substrate correspondingly to boundary lines by which the raw substrate is divided into a plurality of strip-like insulating substrates integrated with each other in parallel, so that said depressed portions are arranged in lines at fixed pitch intervals along said boundary lines, and said lines are formed as scribe lines for breaking said raw substrate into said insulating substrates; wherein the scribe lines have a portion where total volume of the depressed portion per unit length is increased.
A second aspect of the raw substrate is a raw substrate for use for manufacturing insulating substrates in a line-type heater according to the first aspect, wherein each of said scribe lines has an area where pitch intervals of said depressed portions are reduced.
A third aspect of the raw substrate is a raw substrate for use for manufacturing insulating substrates in a line-type heater according to the first aspect, wherein each of said scribe lines has a portion where the depth of said depressed portions is increased.
Namely according to the present invention, provided is a structure of a raw substrate for use for manufacturing insulating substrates in a line-type heater, in which the raw substrate is constituted by a plurality of long strip-like insulating substrates put side by side and integrated with each other, a large number of depressed portions of desired depth are formed by radiation of a laser beam in a surface of the raw substrate correspondingly to boundary lines between the insulating substrates so that the depressed portions are arranged in lines at fixed pitch intervals along the boundary lines, and the lines in which the large number of depressed portions are arranged are formed as scribe lines for breaking the raw substrate into the insulating substrates; characterized in that a portion where the pitch intervals of the depressed portions are reduced is provided over a desired length on the way of each of the scribe lines, or a portion where the depth of the depressed portions is increased is provided over a desired length on the way of each of the scribe lines.
A fourth aspect of the raw substrate is a raw substrate for use for manufacturing insulating substrates in a line-type heater of the present invention, which comprises a large number of depressed portions formed by radiation of a laser beam in a surface of said raw substrate correspondingly to boundary lines by which the raw substrate is divided into a plurality of strip-like insulating substrates integrated with each other in parallel, so that said depressed portions are arranged in lines at fixed pitch intervals along said boundary lines, and said lines are formed as scribe lines for breaking said raw substrate into said insulating substrates; wherein said raw substrate comprises additional depressed portions formed by using the same laser beam in each of the insulating substrates.
A fifth aspect of the raw substrate is a raw substrate for use for manufacturing insulating substrates in a line-type heater according to the fourth aspect, wherein the additional depressed portions are arranged in perpendicular to the scribe lines.
A sixth aspect of the raw substrate is a raw substrate for use for manufacturing insulating substrates in a line-type heater according to the fourth aspect, wherein the additional depressed portions are arranged in parallel to the scribe lines.
A seventh aspect of the method is a method of manufacturing a line-type heater, which comprises the steps of: forming scribe lines of a large number of depressed portions on a surface of a raw substrate, by radiating a laser beam correspondingly to boundary lines by which the raw substrate is divided into a plurality of strip-like insulating substrates integrated with each other in parallel, so that said depressed portions are arranged in lines at fixed pitch intervals along said boundary lines regularly; forming a heating resistance on a surface of each of the strip-like insulating substrates; and dividing the raw substrate into a plurality of strip-like insulating substrates along the scribe lines before or after the step of forming a heating resistance, wherein the step of forming scribe lines comprises a step of irradiating a laser beam so that the scribe lines have a portion where total volume of the depressed portion per unit length is increased.
An eight aspect of the method is a method of manufacturing a line-type heater, according to the seventh aspect, wherein the step of forming scribe lines comprises a step of changing an irradiation pitch of the laser beam so that the each of said scribe lines has an area where pitch intervals of said depressed portions are reduced.
A ninth aspect of the method is a method of manufacturing a line-type heater, according to the seventh aspect, wherein the step of forming scribe lines comprises-a step of changing an irradiation energy of the laser-beam so that the each of said scribe lines has a portion where the depth of said depressed portions is increased.
A tenth aspect of the method is a method of manufacturing a line-type heater, according to the seventh aspect, wherein the step of forming scribe lines comprises a step of forming an additional depressed portion in an area corresponding to each of the insulating substrates.
An eleventh aspect of the method is a method of manufacturing a line-type heater, according to the tenth aspect, wherein the additional depressed portions are arranged in perpendicular to the scribe lines.
A twelfth aspect of the method is a method of manufacturing a line-type heater, according to the tenth aspect, wherein the additional depressed portions are arranged in parallel to the scribe lines.
According to the present invention, a portion where the pitch intervals of the depressed portions are reduced is provided over a desired length on the way of each of the scribe lines, or a portion where the depth of the depressed portions is increased is provided over a desired length on the way of each of the scribe lines. As a result, of the longitudinal side surface of each of the broken insulating substrates, in the portion where the pitch intervals of the depressed portions are reduced, or in the portion where the depth of the depressed portions is increased, the depressed portions are arranged in the state where their pitch intervals are reduced or in the state where their depth is increased, so that the strength in this portion is made lower than the strength in the other portion. Accordingly, when the temperature of the heating resistance film formed on the insulating substrate reaches an abnormal value, the insulating substrate can crack surely in the above-mentioned portion. In addition, since the reduction of the strength is much smaller than that in the conventional case where through holes are formed in the insulating substrate, there is no case that the insulating substrate is snapped easily in the above-mentioned portion when the insulating substrate is broken out from the raw substrate or when the insulating substrate is handled, for example, carried, attached and so on.
Moreover, as stated in the above aspect, a plurality of depressed portions of desired depth are provided by radiation of a laser beam in a portion on the way in a longitudinal direction of each of the insulating substrates and in part in width direction of the insulating substrate, so that the widthwise depressed portions are arranged at desired pitch intervals in a direction perpendicular to the scribe lines. As a result, the strength in the portion which is a part in the longitudinal direction of the insulating substrate and in which a plurality of depressed portions are arranged at desired pitch intervals in the direction perpendicular to the scribe line is made lower than the strength in the other portion in the longitudinal direction of the insulating substrates, that is, the portion where no such a plurality of depressed portions are arranged in the direction perpendicular to the scribe line. Accordingly, when the temperature of the heating resistance film formed on the insulating substrate reaches an abnormal value, the insulating substrate can crack surely in the above-mentioned portion where a plurality of depressed portions are arranged in the direction perpendicular to the scribe line. In addition, since the reduction of the strength is much smaller than that in the conventional case where through holes are formed in the insulating substrate, there is no case that the insulating substrate is snapped easily in the above-mentioned portions when the insulating substrate is broken out from the raw substrate or when the insulating substrate is handled, for example, carried, attached and so on.
Further, as stated in the above aspect, a plurality of depressed portions of desired depth are provided by the radiation of a laser beam in a portion over a part of length on the way of the whole length of each of the insulating substrates and in adjacent to the scribe line so that the plurality of depressed portions are arranged at desired pitch intervals in a direction parallel with the scribe lines. As a result, the strength in the portion of the insulating substrate where a plurality of depressed portions are arranged at desired pitch intervals in the direction parallel with the scribe line is made lower than the strength in the other portion in the longitudinal direction of the insulating substrate, that is, the portion where no such a plurality of depressed portions are arranged in the direction parallel with the scribe line. Accordingly, when the temperature of the heating resistance film formed on the insulating substrate reaches an abnormal value, the insulating substrate can crack surely in the above-mentioned portion where a plurality of depressed portions are arranged in the direction parallel with the scribe line. In addition, since the reduction of the strength is much smaller than that in the conventional case where a through hole is formed in the insulating substrate, there is no case that the insulating substrate is snapped easily in the above-mentioned portion when the insulating substrate is broken out from the raw substrate or when the insulating substrate is handled, for example, carried, attached and so on.